Because you can make this alarm siren that wakes you up gradually as the day
dawns. First, set the switch to position OFF and complete the wiring.

Then, set the switch to ON to turn on the power. Can you hear the siren sound
coming from the speaker?

The siren sounds when you expose the CdS cell to light. When you cast a
shadow over the CdS, the siren sound stops. Like the electronic buzzer in
Project Operational Amplifier Buzzer, the alarm siren
uses a multivibrator, and controls its operation with the CdS.

Turn on the power for this project when you go to bed at night, and sleep
with your room dark. Then, the alarm siren will wake you up the next morning.